Proefschrift_vd_Beek

microphones in the test set-up. They would also have the chance to learn whether they could expect any benefits from the use of these microphones in their personal situations, at work or home. Thirteen people responded and were included in the test. All subjects were postlingually deafened adult users of the Clarion CII cochlear implant, having an average follow-up of 12.3 mo after implantation, ranging from 3–21 mo. The average age was 45.3 yr. All participants used a CIS (Continuous Interleaved Sampling) strategy on CII Platinum Speech Processor (PSP) worn on their bodies. Table 1 shows the patient demographics. The average phoneme score in quiet surroundings equalled 88%, with a range of 67–98%. Table 2 shows the average group results of the listening tests for quiet surroundings and SNR +10, +5, 0 and –5 dB in the standard situation with speech and noise coming from one loudspeaker which had been placed in front of the listener. These listening tests had been taken on a routine base as part of the standard clinical evaluations with speech and noise material from the standard CD. These clinical data can be used as a reference for comparison between a standard clinical test with speech and noise coming from one direction and our new set-up. Five subjects with normal hearing, aged between 22 and 25 were tested in the diffuse noise field set-up for a comparison of the performance of subjects with unimpaired hearing with our CI- patients. Each subject was seated in the imaginary center of the set-up, with the head at the same height as the loudspeaker in front of him or her. The cochlear implant users were allowed to adjust the level of the PSP to the most convenient loudness level based on running speech from the loudspeaker in front at the level used for testing (65 dB SPL) for each microphone array. There was no internal mixing of the signals of the directional microphones with the headpiece microphone. No change to the implant settings or to the position of the head was allowed during the test sequences. To minimize learning effects, the three microphones were tested in random order, based on a Latin square (ABC ACB BCA BAC CAB CBA with A = Headpiece, B = Handymic and C = Linkit). Sufficient lists of words were available, so that we did not have to repeat any list within a single session. Tests were performed in one session of 1.5 hr, with a short break. On average 53 lists were used for one subject to cover all situations. Determination of Speech Reception Threshold Every subject was tested at fixed noise levels: in quiet surroundings, at SNR +10 dB and SNR 0 dB with the headpiece microphone and the two directional microphones. Based on the individual results at +10 dB and 0 dB, extra tests were done for one or two extra fixed SNR ratios (e.g. +5, -5 or -10 dB) in order to obtain data points above and under a 50% phoneme-score. The estimation of the SRT for each individual can be calculated from this data by simple linear interpolation of the percentages found for the levels just above and below 50%. This elaborative procedure was chosen because it was not possible to determine the SRT with an adaptive procedure. The Dutch equivalent of the English HINT-test comprises intelligibility of sentences and thus expects 100% intelligibility. Besides the determination of the SRT of the group, it is of interest to determine the absolute values of the phoneme scores at other SNRs. However, using the approach of score-dependent testing, we would obtain fewer data-points at SNR values of the e.g. +15, +5, -5 and -10 dB. Therefore, the data-points of each

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